The very localised Large Heath occurs in discrete colonies up to about 500-600m above sea-level in open boggy habitats where its main foodplant, Hare's-tail Cotton Grass (Eriophorum vaginatum), grows in abundance. This declining butterfly has suffered from the drainage and destruction of many of its bog habitats. (For further details on this species see http://www.butterfly-conservation.org/).

Status details : Status since 1990 is Rapid increase with a increase of 249%Status over the last 20 years is Stable with a increase of 126%Status over the last 10 years is Stable with a decrease of -56.5%

Log collated index plot

This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in
populations from year to year, and is scaled so that the average index over the whole series is equal to 2
(horizontal line). For greater detail about how this index is derived, click on the green question mark above.

Trend description :This is a species that has significantly increased on UKBMS transects since monitoring began. As with other realtively rare species caution must be taken when interpretting the results given the smaller number of sites, and thus sample size, that this butterfly is recorded at. However, where sufficent data is available the signs are good with stable populations at seven sites and two sites showing increases (Thorne Moors in South Yorkshire, and Whixall fens and Mosses in Clwyd), whilst there is only one site, Taynish on the west coast of Scotland, where numbers have declined.

Phenology plot

Phenology plot

This chart shows the average number of butterflies seen on transects between Arpil and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.

This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.

Coverage

In total, Large Heath has been recorded from 152 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 22 sites, with an average index of 20 individuals per site.

For 11 of these sites, Large Heath has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.

In 2016, 234 individuals were recorded from 6 sites, producing annual indices at 5 of these.

This map shows the trend in abundance at particular transect sites for which data has been received within the last five years. Trends (increasing, declining or stable) are assessed at sites where the species has more than five years of annual index data. Use the option boxes below to view plots for individual sites.